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Title: Modeling of CO 2 sequestration in coal seams: Role of CO 2 -induced coal softening on injectivity, storage efficiency and caprock deformation: Original Research Article: Modeling of CO 2 sequestration in coal seams

An effective and safe operation for sequestration of CO 2 in coal seams requires a clear understanding of injection-induced coupled hydromechanical processes such as the evolution of pore pressure, permeability, and induced caprock deformation. In this study, CO 2 injection into coal seams was studied using a coupled flow-deformation model with a new stress-dependent porosity and permeability model that considers CO 2 -induced coal softening. Based on triaxial compression tests of coal samples extracted from the site of the first series of enhanced coalbed methane field tests in China, a softening phenomenon that a substantial (one-order-of-magnitude) decrease of Young's modulus and an increase of Poisson's ratio with adsorbed CO 2 content was observed. Such softening was considered in the numerical simulation through an exponential relation between elastic properties (Young's modulus and Poisson's ratio) and CO 2 pressure considering that CO 2 content is proportional to the CO 2 pressure. Our results of the numerical simulation show that the softening of the coal strongly affects the CO 2 sequestration performance, first by impeding injectivity and stored volume (cumulative injection) during the first week of injection, and thereafter by softening mediated rebound in permeability that tends to increase injectivity and storage overmore » the longer term. A sensitivity study shows that stronger CO 2 -induced coal softening and higher CO 2 injection pressure contribute synergistically to increase a significant increase of CO 2 injectivity and adsorption, but also result in larger caprock deformations and uplift. This study demonstrates the importance of considering the CO 2 -induced softening when analyzing the performance and environmental impact of CO 2 -sequestration operations in unminable coal seams.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [2]
  1. China Univ. of Mining and Technology, Jiangsu (China); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Earth Sciences Division
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Earth Sciences Division
  3. China Univ. of Mining and Technology, Jiangsu (China)
  4. Southwest Univ. of Science and Technology, Mianyang (China)
Publication Date:
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Greenhouse Gases: Science and Technology
Additional Journal Information:
Journal Volume: 7; Journal Issue: 3; Journal ID: ISSN 2152-3878
Publisher:
Society of Chemical Industry, Wiley
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Fossil Energy (FE), Clean Coal and Carbon (FE-20)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; CO2 sequestration; coal seams; coal softening; caprock deformations
OSTI Identifier:
1379870
Alternate Identifier(s):
OSTI ID: 1401751